Because SALARY is not declared to have NULLs and the employees for whom the
salary is not known are also counted.

9) How do you concatenate the FIRSTNAME and LASTNAME from EMP table to give a
complete name?

SELECT FIRSTNAME || � � || LASTNAME FROM EMP;

10) What is the use of VALUE function?

1. Avoid -ve SQLCODEs by handling nulls and zeroes in computations

2. Substitute a numeric value for any nulls used in computation

11) What is UNION,UNION ALL? �

UNION : eliminates duplicates

UNION ALL: retains duplicates

Both these are used to combine the results of different SELECT
statements.

Suppose I have five SQL SELECT statements connected by UNION/UNION ALL, how
many times should I specify UNION to eliminate the duplicate rows? -

Once.

12) What is the restriction on using UNION in embedded SQL?

It has to be in a CURSOR.

13) In the WHERE clause what is BETWEEN and IN? �

BETWEEN supplies a range of values while IN supplies a list of values.

14) Is BETWEEN inclusive of the range values specified? �

Yes.

15) What is 'LIKE' used for in WHERE clause? What are the wildcard
characters? �

LIKE is used for partial string matches. �%� ( for a string of any character
) and �_� (for any single character ) are the two wild card characters.

16) When do you use a LIKE statement?

To do partial search e.g. to search employee by name, you need not specify
the complete name; using LIKE, you can search for partial string matches.

17) What is the meaning of underscore ( �_� ) in the LIKE statement? �

Match for any single character.

18) What do you accomplish by GROUP BY ... HAVING clause? �

GROUP BY partitions the selected rows on the distinct values of the column on
which you group by.

HAVING selects GROUPs which match the criteria specified

19) Consider the employee table with column PROJECT nullable. How can you get
a list of employees who are not assigned to any project?

SELECT EMPNO

FROM EMP

WHERE PROJECT IS NULL;

20) What is the result of this query if no rows are selected:

SELECT SUM(SALARY)

FROM EMP

WHERE QUAL=�MSC�;

NULL

21) Why SELECT * is not preferred in embedded SQL programs?

For three reasons:

If the table structure is changed ( a field is added ), the program will have
to be modified

Program might retrieve the columns which it might not use, leading on I/O
over head.

The chance of an index only scan is lost.

What are correlated subqueries? -

A subquery in which the inner ( nested ) query refers back to the table in
the outer query. Correlated subqueries must be evaluated for each qualified row
of the outer query that is referred to.

22) What are the issues related with correlated subqueries? �

???

DB2 Interview Questions - PART II

23) What is a cursor? why should it be used? �

Cursor is a programming device that allows the SELECT to find a set of rows
but return them one at a time.

Cursor should be used because the host language can deal with only one row at
a time.

24) How would you retrieve rows from a DB2 table in embedded SQL? �

Either by using the single row SELECT statements, or by using the CURSOR.

Apart from cursor, what other ways are available to you to retrieve a row
from a table in embedded SQL? -

Single row SELECTs.

25) Where would you specify the DECLARE CURSOR statement? �

See answer to next question.

26) How do you specify and use a cursor in a COBOL program? �

Use DECLARE CURSOR statement either in working storage or in procedure
division(before open cursor), to specify the SELECT statement. Then use OPEN,
FETCH rows in a loop and finally CLOSE.

27) What happens when you say OPEN CURSOR?

If there is an ORDER BY clause, rows are fetched, sorted and made available
for the FETCH statement. Other wise simply the cursor is placed on the first
row.

28) Is DECLARE CURSOR executable?

No.

29) Can you have more than one cursor open at any one time in a program ? �

Yes.

30) When you COMMIT, is the cursor closed? - drona db2 interview questions

Yes.

31) How do you leave the cursor open after issuing a COMMIT? ( for DB2 2.3 or
above only )

Use WITH HOLD option in DECLARE CURSOR statement. But, it has not effect in
psuedo-conversational CICS programs.

32) Give the COBOL definition of a VARCHAR field.

A VARCHAR column REMARKS would be defined as follows:

...

10 REMARKS.

49 REMARKS-LEN PIC S9(4) USAGE COMP.

49 REMARKS-TEXT PIC X(1920).

33) What is the physical storage length of each of the following DB2 data
types:

DATE, TIME, TIMESTAMP?

DATE: 4bytes

TIME: 3bytes

TIMESTAMP: 10bytes

34) What is the COBOL picture clause of the following DB2 data types:

DATE, TIME, TIMESTAMP?

DATE: PIC X(10)

TIME : PIC X(08)

TIMESTAMP: PIC X(26)

35) What is the COBOL picture clause for a DB2 column defined as
DECIMAL(11,2)? - Ramesh

PIC S9(9)V99 COMP-3.

Note: In DECIMAL(11,2), 11 indicates the size of the data type and 2
indicates the precision.

36) What is DCLGEN ? -

DeCLarations GENerator: used to create the host language copy books for the
table definitions. Also creates the DECLARE table.

37) What are the contents of a DCLGEN? -

1. EXEC SQL DECLARE TABLE statement which gives the layout of the table/view
in terms of DB2 datatypes.

2. A host language copy book that gives the host variable definitions for the
column names.

38) Is it mandatory to use DCLGEN? If not, why would you use it at all? -

It is not mandatory to use DCLGEN.

Using DCLGEN, helps detect wrongly spelt column names etc. during the
pre-compile stage itself ( because of the DECLARE TABLE ). DCLGEN being a tool,
would generate accurate host variable definitions for the table reducing chances
of error.

39) Is DECLARE TABLE in DCLGEN necessary? Why it used?

It not necessary to have DECLARE TABLE statement in DCLGEN. This is used by
the pre-compiler to validate the table-name, view-name, column name etc., during
pre-compile.

40) Will precompile of an DB2-COBOL program bomb, if DB2 is down?

No. Because the precompiler does not refer to the DB2 catalogue
tables.

41) How is a typical DB2 batch pgm executed ?

1. Use DSN utility to run a DB2 batch program from native TSO. An example is
shown:

DSN SYSTEM(DSP3)

RUN PROGRAM(EDD470BD) PLAN(EDD470BD) LIB('ED 01T.OBJ.LOADLIB')

END

2. Use IKJEFT01 utility program to run the above DSN command in a JCL.

Assuming that a site�s standard is that pgm name = plan name, what is the
easiest way to find out which pgms are affected by change in a table�s structure
?

Query the catalogue tables SYSPLANDEP and SYSPACKDEP.

42) Name some fields from SQLCA.

SQLCODE, SQLERRM, SQLERRD

43) How can you quickly find out the # of rows updated after an update
statement?

Check the value stored in SQLERRD(3).

44) What is EXPLAIN? � drona questions

EXPLAIN is used to display the access path as determined by the optimizer for
a SQL statement. It can be used in SPUFI (for single SQL statement ) or in BIND
step (for embedded SQL ).

45) What do you need to do before you do EXPLAIN?

Make sure that the PLAN_TABLE is created under the AUTHID.

46) Where is the output of EXPLAIN stored? �

In userid.PLAN_TABLE

47) EXPLAIN has output with MATCHCOLS = 0. What does it mean? �

a nonmatching index scan if ACCESSTYPE = I.

48) How do you do the EXPLAIN of a dynamic SQL statement?

1. Use SPUFI or QMF to EXPLAIN the dynamic SQL statement

2. Include EXPLAIN command in the embedded dynamic SQL statements

49) How do you simulate the EXPLAIN of an embedded SQL statement in
SPUFI/QMF? Give an example with a host variable in WHERE clause.)

Use a question mark in place of a host variable ( or an unknown value ).
e.g.

SELECT EMP_NAME

FROM EMP

WHERE EMP_SALARY > ?

DB2 Interview Questions - PART III
www.mainframegurukul.com

50) What are the isolation levels possible ? �

CS: Cursor Stability

RR: Repeatable Read

51) What is the difference between CS and RR isolation levels?

CS: Releases the lock on a page after use

RR: Retains all locks acquired till end of transaction

52) Where do you specify them ?

ISOLATION LEVEL is a parameter for the bind process.

53) When do you specify the isolation level? How?

During the BIND process. ISOLATION ( CS/RR )...

I use CS and update a page. Will the lock be released after I am done with
that page?

No.

54) What are the various locking levels available?

PAGE, TABLE, TABLESPACE

55) How does DB2 determine what lock-size to use?

1. Based on the lock-size given while creating the tablespace

2. Programmer can direct the DB2 what lock-size to use

3. If lock-size ANY is specified, DB2 usually chooses a lock-size of
PAGE

56) What are the disadvantages of PAGE level lock? - RAMESH www.mainframetutorials.com

High resource utilization if large updates are to be done

57) What is lock escalation?

Promoting a PAGE lock-size to table or tablespace lock-size when a
transaction has acquired more locks than specified in NUMLKTS. Locks should be
taken on objects in single tablespace for escalation to occur.

DB2 INTERVIEW QUESTIONS - advertisement

58) What are the various locks available?

SHARE, EXCLUSIVE, UPDATE

59) Can I use LOCK TABLE on a view?

No. To lock a view, take lock on the underlying tables.

60) What is ALTER ? �

SQL command used to change the definition of DB2 objects.

61) What is a DBRM, PLAN ?

DBRM: DataBase Request Module, has the SQL statements extracted from the host
language program by the pre-compiler.

PLAN: A result of the BIND process. It has the executable code for the SQL
statements in the DBRM.

62) What is ACQUIRE/RELEASE in BIND?

Determine the point at which DB2 acquires or releases locks against table and
tablespaces, including intent locks.

63) What else is there in the PLAN apart from the access path? �

PLAN has the executable code for the SQL statements in the host
program

64) What happens to the PLAN if index used by it is dropped?

Plan is marked as invalid. The next time the plan is accessed, it is
rebound.

65) What are PACKAGES ? �

They contain executable code for SQL statements for one DBRM.

66) What are the advantages of using a PACKAGE?

1. Avoid having to bind a large number of DBRM members into a plan

2. Avoid cost of a large bind

3. Avoid the entire transaction being unavailable during bind and automatic
rebind of a plan

4. Minimize fallback complexities if changes result in an error.

67) What is a collection?

a user defined name that is the anchor for packages. It has not physical
existence. Main usage is to group packages.

In SPUFI suppose you want to select max. of 1000 rows , but the select
returns only 200 rows.

68) What are the 2 sqlcodes that are returned? �

100 ( for successful completion of the query ), 0 (for successful COMMIT if
AUTOCOMMIT is set to Yes).

69) How would you print the output of an SQL statement from SPUFI? �

Print the output dataset.

70) How do you pull up a query which was previously saved in QMF ? �

??

71) Lot of updates have been done on a table due to which indexes have gone
haywire. What do you do? �

Looks like index page split has occurred. DO a REORG of the indexes.

72) What is dynamic SQL? �

Dynamic SQL is a SQL statement created at program execution time.

73) When is the access path determined for dynamic SQL? �

At run time, when the PREPARE statement is issued.

74) Suppose I have a program which uses a dynamic SQL and it has been
performing well till now. Off late, I find that the performance has
deteriorated. What happened? �

Probably RUN STATS is not done and the program is using a wrong index due to
incorrect stats.

Probably RUNSTATS is done and optimizer has chosen a wrong access path based
on the latest statistics.

DB2 Interview Questions - PART IV
www.mainframegurukul.com

75) How does DB2 store NULL physically?

as an extra-byte prefix to the column value. physically, the nul prefix is
Hex �00� if the value is present and Hex �FF� if it is not.

76) How do you retrieve the data from a nullable column? �

Use null indicators. Syntax ... INTO :HOSTVAR:NULLIND

77) What is the picture clause of the null indicator variable? �

S9(4) COMP.

78) What does it mean if the null indicator has -1, 0, -2? �

-1 : the field is null

0 : the field is not null

-2 : the field value is truncated

79) How do you insert a record with a nullable column?

To insert a NULL, move -1 to the null indicator

To insert a valid value, move 0 to the null indicator

80) What is RUNSTATS? �

A DB2 utility used to collect statistics about the data values in tables
which can be used by the optimizer to decide the access path. It also collects
statistics used for space management. These statistics are stored in DB2 catalog
tables.

81) When will you chose to run RUNSTATS?

After a load, or after mass updates, inserts, deletes, or after REORG.

82) Give some example of statistics collected during RUNSTATS?

# of rows in the table

Percent of rows in clustering sequence

# of distinct values of indexed column

# of rows moved to a nearby/farway page due to row length increase

83) What is REORG? When is it used?

REORG reorganizes data on physical storage to reclutser rows, positioning
overflowed rows in their proper sequence, to reclaim space, to restore free
space. It is used after heavy updates, inserts and delete activity and after
segments of a segmented tablespace have become fragmented.

84) What is IMAGECOPY ? �

It is full backup of a DB2 table which can be used in recovery.

85) When do you use the IMAGECOPY? �

To take routine backup of tables

After a LOAD with LOG NO

After REORG with LOG NO

86) What is COPY PENDING status?

A state in which, an image copy on a table needs to be taken, In this status,
the table is available only for queries. You cannot update this table. To remove
the COPY PENDING status, you take an image copy or use REPAIR utility.

87) What is CHECK PENDING ?

When a table is LOADed with ENFORCE NO option, then the table is left in
CHECK PENDING status. It means that the LOAD utility did not perform constraint
checking.

88) What is QUIESCE?

A QUIESCE flushes all DB2 buffers on to the disk. This gives a correct
snapshot of the database and should be used before and after any IMAGECOPY to
maintain consistency.

89) What is a clustering index ? �

Causes the data rows to be stored in the order specified in the index. A
mandatory index defined on a partitioned table space.

90) How many clustering indexes can be defined for a table?

Only one.

91) What is the difference between primary key & unique index ?

Primary : a relational database constraint. Primary key consists of one or
more columns that uniquely identify a row in the table. For a normalized
relation, there is one designated primary key.

Unique index: a physical object that stores only unique values. There can be
one or more unique indexes on a table.

92) What is sqlcode -922 ?

Authorization failure

93) What is sqlcode -811?

SELECT statement has resulted in retrieval of more than one row.

94) What does the sqlcode of -818 pertain to? �

This is generated when the consistency tokens in the DBRM and the load module
are different.

95) Are views updateable ?

Not all of them. Some views are updateable e.g. single table view with all
the fields or mandatory fields. Examples of non-updateable views are views which
are joins, views that contain aggregate functions(such as MIN), and views that
have GROUP BY clause.

96) If I have a view which is a join of two or more tables, can this view be
updateable? �

No.

97) What are the 4 environments which can access DB2 ?

TSO, CICS, IMS and BATCH

98) What is an inner join, and an outer join ?

Inner Join: combine information from two or more tables by comparing all
values that meet the search criteria in the designated column or columns of on e
table with all the clause in corresponding columns of the other table or tables.
This kind of join which involve a match in both columns are called inner
joins.

Outer join is one in which you want both matching and non matching rows to be
returned. DB2 has no specific operator for outer joins, it can be simulated by
combining a join and a correlated sub query with a UNION.

99) What is FREEPAGE and PCTFREE in TABLESPACE creation?

PCTFREE: percentage of each page to be left free

FREEPAGE: Number of pages to be loaded with data between each free
page

100) What are simple, segmented and partitioned table spaces ?

Simple Tablespace:

Can contain one or more tables

Rows from multiple tables can be interleaved on a page under the DBAs control
and maintenance

Segmented Tablespace:

Can contain one or more tables

Tablespace is divided into segments of 4 to 64 pages in increments of 4
pages. Each segment is dedicated to single table. A table can occupy multiple
segments

Partitioned Tablespace:

Can contain one table

Tablespace is divided into parts and each part is put in a separate VSAM
dataset.

101) What is filter factor?

one divided by the number of distinct values of a column.

102) What is index cardinality? �

The number of distinct values a column or columns contain.

103) What is a synonym ?

Synonym is an alternate name for a table or view used mainly to hide the
leading qualifier of a table or view.. A synonym is accessible only by the
creator.

104) What is the difference between SYNONYM and ALIAS?

SYNONYM: is dropped when the table or tablespace is dropped. Synonym is
available only to the creator.

ALIAS: is retained even if table or tablespace is dropped. ALIAS can be
created even if the table does not exist. It is used mainly in distributed
environment to hide the location info from programs. Alias is a global object
& is available to all.

105) What do you mean by NOT NULL WITH DEFAULT? When will you use it?

This column cannot have nulls and while insertion, if no value is supplied
then it wil have zeroes, spaces or date/time depending on whether it is numeric,
character or date/time.

Use it when you do not want to have nulls but at the same time cannot give
values all the time you insert this row.

106) What do you mean by NOT NULL? When will you use it?

The column cannot have nulls. Use it for key fields.

107) When would you prefer to use VARCHAR?

When a column which contains long text, e.g. remarks, notes, may have in most
cases less than 50% of the maximum length.

108) What are the disadvantages of using VARCHAR?

1. Can lead to high space utilization if most of the values are close to
maximum.

2. Positioning of VARCHAR column has to be done carefully as it has
performance implications.

3. Relocation of rows to different pages can lead to more I/Os on
retrieval.

109) How do I create a table MANAGER ( EMP#, MANAGER) where MANAGER is a
foreign key which references to EMP# in the same table? Give the exact DDL.

First CREATE MANAGER table with EMP# as the primary key. Then ALTER it to
define the foreign key.

When is the authorization check on DB2 objects done - at BIND time or run
time?

At run time.

110) What is auditing?

Recording SQL statements that access a table. Specified at table creation
time or through alter.